What do i need to do if I crossfire 2 graphics cards.?

Hello,
I’d love to know just what exactly I want to do when mix firing a pair of graphics playing cards on my system.
I currently use a single GFX unit card:ATI Radeon 5770 1gb
My friend is going to give my home his GFX cartomancy:ATI Radeon 4850 1gb

Will this be a challenge considering the card designs Do they have to be identical to crossfire

Our current specs are:
Operating System
MS Windows SEVERAL Ultimate 64-bit SP1
CPU
Intel Center i7 950 3.07GHz
Bloomfield 45nm Technology
RAM
10.0GB Triple-Channel DDR3 532MHz (7-7-7-20)
Motherboard
Gigabyte Technological innovation Co., Ltd.X58A-UD3R (Socket 1366)
Graphics
Panasonic-TV (1920x108050Hz)
ATI Radeon HARLEY-DAVIDSON 5700 Series
Difficult Drives
488GB Hitachi Hitachi HDP725050GLA360 ATA Apparatus (SATA)
488GB Seagate ST3500413AS ATA Apparatus (SATA)
Optical Drives
ATAPI MOVIE A DH16AAL SCSI CdRom Device
Audio
Realtek Hd Audio

I would like to realize asap as I want to employ FRAPS in order to record the actual upcoming FPS “Brink” on the fairly fair resolution without having FRAPS lagging that up.

THANKS

if people wanna use a crossfire when using the 5770 you’ll need another 5770 or even a 5750.The 4850 defintely won’t be compatible for it.